ATLANTA — Georgia would loosen rules meant to prevent hog manure from washing into streams and rivers under a proposal before regulators, but critics argue environmental harm would come from the plan touted by backers as a way to help level the economic playing field.

Members of the state Board of Natural Resources today are to discuss the proposal, which would raise the threshold at which farmers must comply with tougher and more expensive environmental rules from 7,500 pigs to 12,500 pigs for animals weighing 55 pounds or more. The same threshold for hogs weighing less than 55 pounds would rise from 30,000 to 50,000 pigs. A vote is expected before the end of the year.

Agriculture industry leaders say treating hogs differently from other livestock unfairly deters expansion in the pork industry. They say changing the rules will not result in additional pollution.

“The real question is why are we treating swine different than other types of livestock produced in the state of Georgia?” said Bryan Tolar, president of the Georgia Agribusiness Council, a lobbying group for the farming industry. “We’ve been asking that question for a long time.”

Environmental groups say the changes are part of continuing pressure to roll back environmental rules to the benefit of industry.

“This was a very deliberate decision to strike a balance between allowing this type of livestock production in Georgia but also putting reasonable safeguards in place to prevent severe water degradation,” said Gil Rogers, an attorney for the Southern Environmental Law Center, which opposes the change.

Hog farmers are allowed to collect manure in waste lagoons, then spray it as a crop fertilizer on nearby fields. If the system is properly designed, growing plants soak up the waste nutrients, helping to dispose of the manure.

There can be problems. Georgia leaders moved to tighten the state’s rules in 1999 after Hurricane Floyd dumped almost two feet of rain on North Carolina, flooding and damaging waste lagoons. That hog manure — along with lots of other runoff — washed into streams and rivers.

“We’ve just seen the disastrous effect of these concentrated hog facilities” in eastern North Carolina, said Mark Woodall, chair of the Georgia chapter of the Sierra Club. “We just think it’s a terrible threat to the water quality of all of rural Georgia.”

The DNR board eased the rules in 2012, allowing smaller pig farmers to operate under a less-strict regimen. The last change and the current proposal are supported by Agriculture Commissioner Gary Black, a former agriculture lobbyist whose department both promotes Georgia’s agricultural economy and regulates hog farms.

“This proposal allows for a balance between maintaining the current environmental standards, while at the same time allowing the swine industry to become more comparable to other livestock and poultry productions in Georgia, as well as across the Southeast,” Black’s spokeswoman Mary Kathryn Yearta said.

State officials have not studied the economic impact of changing the rules. But the stricter requirements do impose added costs on farmers. Of course, a spill would results in costs, too. Larger operations must have three wells to monitor for pollution, which would be expensive, said Charles Griffin, executive vice president of the Georgia Pork Producers Association.

The waste lagoons of a large farm must have an airtight cap. Farmers must inject the waste below ground, not spray into onto fields. Big operations must also demonstrate they have enough money to clean up a hog farm in case authorities shutter it or it goes out of business.

Griffin said the requirements would make it too expensive to start a large farm.

“That’s just another way of saying, ‘No, we’re not going to do it,’” he said.

The hog farms in Georgia are relatively small. State agriculture officials oversee 31 hog farms in Georgia and none of them are large enough to fall under the strictest rules, according to state records.

Mark Risse, an agricultural engineer at the University of Georgia who studies waste issues, said he occasionally gets calls from firms interested in building hog farms in Georgia. He said falling profit margins have encouraged the agriculture industry toward consolidating into fewer but larger farms. Larger livestock farms benefit from having lower average costs than small operations, which keeps prices down.

“They wouldn’t have to do those things in any other state in the U.S., so essentially it blocks any operation of that size from coming to Georgia,” he said.

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